1. Field of the Invention This invention relates to a laser light irradiation apparatus, which irradiates laser light to living tissues of an animal such as a human body for use an incision, vaporization of the living tissues or a thermal therapy and in case of widening a narrow path of the living tissues such as a stricture part caused by cholesterol formed in the blood vessel of the human.
2. Prior Art
Medical treatments such as incisions of living tissues of animal organisms by irradiation with laser light are now conspicuous due to its ability of hemostasis in these.
It had been the conventional method that the laser light was irradiated from the fore end of an optical fiber retained out of contact with the living tissues. But this method causes severe damage to the fore end portion of the optical fiber. Therefore, a method using a contact probe which has been utilized lately is as follows:
First, laser light is transmitted into an optical fiber, whose fore end portion locates adjacent to treated living tissues. Next, the laser light fed out from the optical fiber is fed into an emitting probe, which may or may not contact the living tissues. Then, the laser light is emitted from the surface of the probe to be irradiated against the living tissues. In this case, the probe should be brought into contact with the living tissues (hereafter "living tissue" is sometimes expressed by "tissue" only).
The applicant developed many kinds of contact probes which are utilized for various purposes.
On the other hand, the applicant proposed (Laid-open No. 2-34161) in Japartese Patent Application No. 63-171688, a laser light medical treatment equipment for burning off a stricture part caused by cholesterol formed on the inner wall of a blood vessel.
Before this invention, that is Japartese Patent Application No. 63-171688, for the treatment for the stricture part, a heat wire probe was inserted into the stricture part. Then, since the heat wire probe was heated as a whole, there was a risk that a normal blood vessel other than the stricture part was damaged. Therefore, in order to prevent the normal blood vessel from being damaged, the laser light medical treatment equipment of this invention was proposed. According to this equipment, while a laser light emitting probe is progressed through the blood vessel to locate before the stricture part formed in the blood vessel, the laser light is emitted so as to be irradiated against only the stricture part, which is beyond the probe.
Further, lately, a localized thermal therapy is drawing special attention as a carcinostatic therapy. According to this method, cancer tissues are destroyed by keeping the cancer tissues at a temperature of about 42.degree.-44.degree. C. for 10-25 minutes by laser light irradiation. The effectiveness of this method has been reported by the inventors in the bulletin of Japart Society of Laser Medicine. vol. 6, No. 3 (January 1986), pp. 71-76 & 347-350.
On the other hand, considerable attention has been paid to laser-chemical therapies including the method reported in 1987 by Dougherty et al of the United States. According to this method, 48 hours after an intravenous injection of a hematoporphyrin derivative (HpD), weak laser-light such as argon laser or argon pigment laser is irradiated against a target area of the treatment. Whereupon oxygen of the primary term which has a strong carcinostatic action is produced by HpD. Since then, there have been published various reports in this regard, including the one in the bulletin of Japart Society of Laser Medicine, vol. 6, No. 3 (January 1986), pp 113-116. In this connection, it has also been known in the art to use "pheophobide a" as a photo-reactant. Further, recently, YAG laser has been put into use as a laser-light source.
In the above mentioned medical treatment, it is important that the laser light is irradiated uniformly for the cancer tissues and, in case of the thermal therapy, it is particularly important that the cancer tissues are heated uniformly.
Further, for heating the tissues uniformly, the applicant disclosed in Japartese Patent Application Laid-Open No. 63-216579, that an apparatus has plural number of laser light emitters and an equipment for adjusting the power level of the laser light impinging into the emitters.
If laser light is irradiated against the tissues from an optical fiber directly or through the intermediary of a contact probe, the power level of the laser light irradiated against the tissues is the largest at a center position of an irradiated area on the surface of the tissues. The center position is contacted by the center of the optical fiber or that of the contact probe, then, the power level is lowered as a position on the surface of the tissues parts away from the above mentioned center position.
For example, as shown in FIG. 8, when the laser light is irradiated against the tissues M with a contact probe P, in the temperature distribution of this figure, there is a peak at its center position and in the both sides in relation to this peak, the level is lowered gradually away from this peak. If the power level of the laser light is raised, the size of this temperature distribution is also enlarged to be a substantial similar figure. However, the power level of the laser light is increased to an excess level, the tissues corresponding to the peak of the temperature distribution are damaged seriously. Accordingly, it is impossible that enlarge an irradiation area by only adjusting of the power level of the laser light.
Therefore, it is difficult to irradiate the laser light uniformly, and particularly more difficult to irradiate the laser light uniformly against the tissues having broad area. Accordingly, within the* limit of the predetermined power level of the laser light, laser light irradiation against each small part of the tissues should be repeated many times in order to carry out the irradiation against all of the treated tissues over a broad area. As a result, a medical operation cannot be carried out quickly.
Under these circumstances, as described before, the applicant proposed in Japartese Patent Application Laid-Open No. 63-216579 that the plural number of probes as the laser light emitters are provided and the laser light is irradiated from each probe simultaneously.
Although the laser light can be irradiated against the tissues having a broad area to some degree by provision of the plural number of laser light emitting probes, the necessity of a number of probes causes the following problem.
For forming the uniform temperature distribution on the irradiated tissues, the probes should be located at precise positions respectively so as to be contacted with the tissues uniformly. Therefore, the medical operation cannot be carried out quickly due to difficulties in precisely locating the probes. On the other hand, since each optical fiber should correspond to each probe, the size of the apparatus is large. Accordingly, this apparatus cannot be used for a medical treatment in a narrow path in the tissues such as a catheter in a blood vessel.
On the other hand, in case of a treatment for a so-called angio-plasty, which means burning off the stricture part formed on the inner surface of the blood vessel to widen the inside of the blood vessel, as described before, the applicant proposed the laser light irradiation probe. In this case, the probe can be used instead of the conventional heat wire probe and is inserted into the blood vessel along the flexible guide wire, which was inserted into the blood vessel previously. Further, in an embodiment of this proposal, in order to prevent the guide wire from being damaged by the laser light irradiation, the guide wire is placed so as to be deflected from the axis of the probe.
However, as shown in FIG. 13, deflection of the guide wire in relation to the axis of the probe causes a following problem. When a probe P is progressed in the blood vessel until the probe P reaches at a bending part, due to the deflection of the guide wire, the probe P should be forced further in the blood vessel against the original bending part. Therefore, the bending manner at this original bending part of the blood vessel is set to be changed to another bending manner. In this case, when the laser light is irradiated against the stricture part m, there is the risk of breaking of the wall of the normal part of the blood vessel BV other than the stricture part m or so-called perforation there.
The energy distribution of the laser light irradiation from the probe and the above mentioned temperature distribution shown in FIG. 8 have a common characterization. That is to say, there is a peak at its center position and at both sides in relation to this peak, the power level of laser light irradiation is lowered. Therefore, while the center of the stricture part m is completely burnt off, the inner wall of the stricture part m, which is away from the center, often still remains not burnt off. Accordingly, the power level of the laser light should be raised in order to burn off the whole stricture part completely. However, if a normal part of the inner wall of the blood vessel faces the center of the emitting face of the probe due to the bending of the blood vessel, there is a risk that the normal part of the vessel may be burned during treatment.